Air pollution caused by exhaust fumes from automobiles has recently become a global problem. Hence, there has been an increased movement toward environmental protection throughout the world. As a means for solving such a problem, an electric vehicle using electricity as its power source and a hybrid vehicle combining an engine and an electric motor have been introduced. Thus, the development of a battery with increased capacity and power, which can be mounted in the electric and hybrid vehicles, is fast becoming important in the automobile industry.
In order to develop such a battery with high capacity and power, an electrode area of the battery must be quite large or a number of cell elements must be stacked upon one another.
However, when the cell elements are stacked, a heat dissipating property of the battery may be deteriorated due to the increased thickness of the battery. That is, when a charging/discharging operation is repeated at a high current, the heat generated by an inner resistance of the battery cannot be rapidly dissipated. Thus, the temperature of the battery inevitably increases to an excessive level. As such, when the heat dissipating property of the battery deteriorates, it may reduce the power or service life of the battery.
For example, Japanese Laid-Open Patent Publication Nos. 2000-100471 and 2000-195495 disclose a bipolar-type battery having a structure wherein bipolar-type electrodes (an electrode wherein a cathode active material layer, a collector and an anode active material layer are stacked in that order) and separators are alternately stacked upon one another. In such a battery, the amount of heat generation is quite large in the cathode active material layer and the anode active material layer. Therefore, when the high capacity and power are required, this is likely to increase the temperature within the battery to thereby deteriorate the heat dissipating property. Consequently, the electrolyte and other components included in the battery are likely to become deteriorated.
Despite the above-described problems of the batteries currently existing in the art, no research or study is presently underway so as to protect the elements of the battery structure from heat.